Institute of Electrical and Electronics Engineers (IEEE) 802.11 is a set of physical and Media Access Control (MAC) specifications for implementing Wireless Local Area Network (WLAN) communications. These specifications provide the basis for wireless network products using the Wi-Fi brand managed and defined by the Wi-Fi Alliance. The specifications define the use of the 2.400-2.500 GHz as well as the 4.915-5.825 GHz bands. These spectrum bands are commonly referred to as the 2.4 GHz and 5 GHz bands. Each spectrum is subdivided into channels with a center frequency and bandwidth. The 2.4 GHz band is divided into 14 channels spaced 5 MHz apart, though some countries regulate the availability of these channels. The 5 GHz band is more heavily regulated than the 2.4 GHz band and the spacing of channels varies across the spectrum with a minimum of a 5 MHz spacing dependent on the regulations of the respective country or territory.
WLAN devices are currently being deployed in diverse environments. These environments are characterized by the existence of many Access Points (APs) and non-AP stations (STAs) in geographically limited areas. Increased interference from neighboring devices gives rise to performance degradation. Additionally, WLAN devices are increasingly required to support a variety of applications such as video, cloud access, and offloading. Video traffic, in particular, is expected to be the dominant type of traffic in WLAN deployments. With the real-time requirements of some of these applications, WLAN users demand improved performance.
In a task group called IEEE 802.11ax, High Efficiency WLAN (HEW) standardization is under discussion. The HEW aims at improving performance felt by users demanding high-capacity and high-rate services. The HEW may support uplink (UL) and downlink (DL) multi-user (MU) simultaneous transmissions, which includes Multi-User Multiple-Input Multiple-Output (MU-MIMO) and Orthogonal Frequency Division Multiple Access (OFDMA) transmissions.
Link adaptation is a technique for adapting parameters of a wireless communications link between a transmitting WLAN device and a receiving WLAN device based on measurements of the current link quality in order to maximize transmission rate. One technique by which link adaptation can be achieved is through a Modulation Coding Scheme (MCS) feedback procedure, where the receiving WLAN device provides feedback to the transmitting WLAN device regarding a recommended MCS that the transmitting STA may use when transmitting to the receiving STA. In IEEE 802.11 systems, MCS feedback may be provided as part of the MAC header of a frame. However, existing IEEE 802.11 systems do not provide an appropriate reference for the transmitting STA to properly interpret and utilize the MCS feedback.